全文获取类型
收费全文 | 415篇 |
免费 | 9篇 |
国内免费 | 3篇 |
专业分类
安全科学 | 15篇 |
废物处理 | 5篇 |
环保管理 | 42篇 |
综合类 | 169篇 |
基础理论 | 94篇 |
环境理论 | 1篇 |
污染及防治 | 69篇 |
评价与监测 | 13篇 |
社会与环境 | 12篇 |
灾害及防治 | 7篇 |
出版年
2023年 | 6篇 |
2021年 | 5篇 |
2020年 | 5篇 |
2018年 | 7篇 |
2017年 | 4篇 |
2016年 | 12篇 |
2015年 | 6篇 |
2014年 | 8篇 |
2013年 | 19篇 |
2012年 | 17篇 |
2011年 | 20篇 |
2010年 | 14篇 |
2009年 | 16篇 |
2008年 | 15篇 |
2007年 | 18篇 |
2006年 | 22篇 |
2005年 | 6篇 |
2004年 | 7篇 |
2002年 | 12篇 |
2001年 | 8篇 |
2000年 | 6篇 |
1999年 | 12篇 |
1998年 | 5篇 |
1997年 | 7篇 |
1992年 | 5篇 |
1989年 | 4篇 |
1984年 | 5篇 |
1982年 | 6篇 |
1981年 | 3篇 |
1974年 | 5篇 |
1971年 | 4篇 |
1969年 | 3篇 |
1968年 | 3篇 |
1967年 | 6篇 |
1966年 | 4篇 |
1965年 | 4篇 |
1964年 | 4篇 |
1961年 | 7篇 |
1960年 | 4篇 |
1957年 | 5篇 |
1956年 | 4篇 |
1955年 | 3篇 |
1948年 | 4篇 |
1940年 | 3篇 |
1937年 | 3篇 |
1928年 | 3篇 |
1927年 | 3篇 |
1920年 | 5篇 |
1916年 | 3篇 |
1913年 | 3篇 |
排序方式: 共有427条查询结果,搜索用时 15 毫秒
1.
Consensus on the evolutionary position of turtles within the amniote phylogeny has eluded evolutionary biologists for more than a century. This phylogenetic problem has remained unsolved partly because turtles have such a unique morphology that only few characters can be used to link them with any other group of amniotes. Among the many alternative hypotheses that have been postulated to explain the origin and phylogenetic relationships of turtles, a general agreement among paleontologists emerged in favoring the placement of turtles as the only living survivors of the anapsid reptiles (those that lack temporal fenestrae in the skull). However, recent morphological and molecular studies have radically changed our view of amniote phylogenetic relationships, and evidence is accumulating that supports the diapsid affinities of turtles. Molecular studies favor archosaurs (crocodiles and birds) as the living sister group of turtles, whereas morphological studies support lepidosaurs (tuatara, lizards, and snakes) as the closest living relatives of turtles. Accepting these hypotheses implies that turtles cannot be viewed any longer as primitive reptiles, and that they might have lost the temporal holes in the skull secondarily rather than never having had them. 相似文献
2.
3.
A survey is given on fluid-dynamic effects caused by the structure and properties of biological surfaces. It is demonstrated
that the results of investigations aiming at technological applications can also provide insights into biophysical phenomena.
Techniques are described both for reducing wall shear stresses and for controlling boundary-layer separation. (a) Wall shear
stress reduction was investigated experimentally for various riblet surfaces including a shark skin replica. The latter consists
of 800 plastic model scales with compliant anchoring. Hairy surfaces are also considered, and surfaces in which the no-slip
condition is modified. Self-cleaning surfaces such as that of lotus leaves represent an interesting option to avoid fluid-dynamic
deterioration by the agglomeration of dirt. An example of technological implementation is discussed for riblets in long-range
commercial aircraft. (b) Separation control is also an important issue in biology. After a few brief comments on vortex generators,
the mechanism of separation control by bird feathers is described in detail. Self-activated movable flaps (=artificial bird
feathers) represent a high-lift system enhancing the maximum lift of airfoils by about 20%. This is achieved without perceivable
deleterious effects under cruise conditions. Finally, flight experiments on an aircraft with laminar wing and movable flaps
are presented. 相似文献
4.
Dedicated to Professor H. J. Berthold, Hannover, on the occasion of his 65th birthday. 相似文献
5.
This paper develops a method for identifying and assessing long-term supply risks for mineral raw materials. The method is based on a combined evaluation of past and future supply and demand trends. By analysing raw material boom and bust cycles over the past 50 years, we have quantified indicators and defined benchmarks for identifying critical market situations. By applying the method, risks for supply shortage may be identified at an early stage. In addition, a numerical evaluation model has been developed for better comparison between various mineral raw materials. Compared to other assessment methods this method uses specific benchmarks for each raw material to better assess supply risks. The method is embedded within a systematic and comprehensive analytical approach. 相似文献
6.
Effects of environmental methylmercury on the health of wild birds, mammals, and fish 总被引:18,自引:0,他引:18
Wild piscivorous fish, mammals, and birds may be at risk for elevated dietary methylmercury intake and toxicity. In controlled feeding studies, the consumption of diets that contained Hg (as methylmercury) at environmentally realistic concentrations resulted in a range of toxic effects in fish, birds, and mammals, including behavioral, neurochemical, hormonal, and reproductive changes. Limited field-based studies, especially with certain wild piscivorous bird species, e.g., the common loon, corroborated laboratory-based results, demonstrating significant relations between methylmercury exposure and various indicators of methylmercury toxicity, including reproductive impairment. Potential population effects in fish and wildlife resulting from dietary methylmercury exposure are expected to vary as a function of species life history, as well as regional differences in fish-Hg concentrations, which, in turn, are influenced by differences in Hg deposition and environmental methylation rates. However, population modeling suggests that reductions in Hg emissions could have substantial benefits for some common loon populations that are currently experiencing elevated methylmercury exposure. Predicted benefits would be mediated primarily through improved hatching success and development of hatchlings to maturity as Hg concentrations in prey fish decline. Other piscivorous species may also benefit from decreased Hg exposure but have not been as extensively studied as the common loon. 相似文献
7.
In the event of a natural or anthropogenic disturbance, environmental resource managers require a reliable tool to quickly
assess the spatial extent of potential damage to the seagrass resource. The temporal availability of the Landsat 5 Thematic
Mapper (TM) imagery provided a suitable option to detect and assess damage of the submerged aquatic vegetation (SAV). This
study examined Landsat TM imagery classification techniques to create two-class (SAV presence/absence) and three-class (SAV
estimated coverage) SAV maps of the seagrass resource. The Mahalanobis Distance method achieved the highest overall accuracy
(86%) and validation accuracy (68%) for delineating the seagrass resource (two-class SAV map). The Maximum Likelihood method
achieved the highest overall accuracy (74%) and validation accuracy (70%) for delineating the seagrass resource three-class
SAV map. The Landsat 5 TM imagery classification provided a seagrass resource map product with similar accuracy to the aerial
photointerpretation maps (validation accuracy 71%). The results support the application of remote sensing methods to analyze
the spatial extent of the seagrass resource. 相似文献
8.
Ninon F. V. Meyer Ricardo Moreno Christopher Sutherland J. Antonio de la Torre Helen J. Esser Christopher A. Jordan Melva Olmos Josué Ortega Rafael Reyna-Hurtado Samuel Valdes Patrick A. Jansen 《Conservation biology》2020,34(1):207-219
Habitat fragmentation is a primary driver of wildlife loss, and establishment of biological corridors is a common strategy to mitigate this problem. A flagship example is the Mesoamerican Biological Corridor (MBC), which aims to connect protected forest areas between Mexico and Panama to allow dispersal and gene flow of forest organisms. Because forests across Central America have continued to degrade, the functioning of the MBC has been questioned, but reliable estimates of species occurrence were unavailable. Large mammals are suitable indicators of forest functioning, so we assessed their conservation status across the Isthmus of Panama, the narrowest section of the MBC. We used large-scale camera-trap surveys and hierarchical multispecies occupancy models in a Bayesian framework to estimate the occupancy of 9 medium to large mammals and developed an occupancy-weighted connectivity metric to evaluate species-specific functional connectivity. White-lipped peccary (Tayassu pecari), jaguar (Panthera onca), giant anteater (Myrmecophaga tridactyla), white-tailed deer (Odocoileus virginianus), and tapir (Tapirus bairdii) had low expected occupancy along the MBC in Panama. Puma (Puma concolor), red brocket deer (Mazama temama), ocelot (Leopardus pardalis), and collared peccary (Pecari tajacu), which are more adaptable, had higher occupancy, even in areas with low forest cover near infrastructure. However, the majority of species were subject to ≥1 gap that was larger than their known dispersal distances, suggesting poor connectivity along the MBC in Panama. Based on our results, forests in Darien, Donoso–Santa Fe, and La Amistad International Park are critical for survival of large terrestrial mammals in Panama and 2 areas need restoration. 相似文献
9.
10.
The persistence of pharmaceuticals, hormones, and household and industrial chemicals through a pure-oxygen activated sludge, nitrification, denitrification wastewater treatment facility was evaluated. Of the 125 micropollutants that were tested in this study, 55 compounds were detected in the untreated wastewater, and 27 compounds were detected in the disinfected effluent. The persistent compounds included surfactants, fire-retardant chemicals, pesticides, fragrance compounds, hormones, and one pharmaceutical. Physical-chemical properties of micropollutants that affected partitioning onto wastewater solids included vapor pressure and octanol-water partition coefficients. 相似文献